June 30, 2006 | David F. Coppedge

Paper View:  Why SETI Hears Only a “Great Silence”

Enrico Fermi posed a curious question in 1950: “Where is everybody?”  If life emerges on planets as a consequence of evolution, there should be other intelligent civilizations out there, and some of them must have colonized other worlds.  He thought there must have been plenty of time for galactic colonizers to achieve technologies far beyond our own by billions of years, and therefore to have reached every corner of the Galaxy by now, including Earth.  Where are they?  This innocuous question, named “Fermi’s Paradox” (though others had asked it, too) has troubled advocates of the Search for Extraterrestrial Intelligence (SETI) ever since.  Though SETI technicians patiently eavesdrop on more and more stars each year in the half-century since SETI began, the Great Silence seems ominous.
    Milan M. Cirkovic and Robert J. Bradbury think they know why.  Their ideas, published in New Astronomy July 2006,1 call for nothing less than a complete overhaul of SETI thinking:

Hereby, we would like to propose a novel solution, based on the astrophysical properties of our Galactic environment on large scales, as well as some economic and informational aspects of the presumed advanced technological civilizations (henceforth ATCs).  In doing so, we will suggest a radically new perspective on the entire SETI endeavor.

Traditional SETI, listening for radio signals from biological life, is “fundamentally flawed,” they claim.  Think post-biological.  Life will not remain content with the limitations of flesh, they reason.  Borrowing from the speculations of science historian Steven J. Dick, they believe biology will eventually give way to technology.  Advanced technical civilizations will be composed of machines.  They quote Dick:

In sorting priorities, I adopt what I term the central principle of cultural evolution, which I refer to as the Intelligence Principle: the maintenance, improvement and perpetuation of knowledge and intelligence is the central driving force of cultural evolution, and that to the extent intelligence can be improved, it will be improved.

Not “whatever can go wrong, will go wrong,” in other words.  At least until the universe runs down, the Intelligence Principle will triumph over Murphy’s Law.  This is the foundational principle of their proposal.  Life will gravitate toward maximum information processing, subject to the constraints of physical laws.

A natural extension of the Intelligence Principle is what can be called the digital perspective on astrobiology: After a particular threshold complexity is reached, the relevant relations between existent entities are characterized by requirements of computation and information processing.  It is related to the emergent computational concepts not only in biology, but in other fields such as fundamental physics, cosmology, neuroscience, and social sciences.

Here’s a brief synopsis of their scenario.  Life emerges on a planet, evolves to a state of intelligence, then gravitates toward more efficient information processing and computation, till it transcends the biological and becomes strictly technological.  A machine civilization is not going to care about communicating with beings like us.  Its priority will be to maximize information processing.  To do this, the entities will have to have to migrate from the places where they first evolved as biological life forms.  This is due to simple constraints of physics.  The warmth of a summer sun may be valuable to biological organisms like us, but heat is an enemy of computation.  Galaxies have a galactic temperature gradient: hot at the center, cooler at the edges.  It’s at the outskirts of the galaxy, therefore, where a machine civilization would migrate.  That, however, is not where traditional SETI is looking, and that is the reason for the Great Silence.
    In their scenario, we need to drastically modify our search strategy.  Whether artifacts of technology would be detectable at the edges of the Milky Way or external galaxies, they are not sure.  Perhaps aliens would send inscriptions (see 09/01/2004).  They are quite certain, though, that radio is not on the broadcast schedule:

We conclude that the conventional radio SETI assuming beamed broadcasts from targets – selected exclusively on the basis of the old-fashioned biological paradigm – within the vicinity of our Solar System … is ill-founded and has minuscule chances of success on the present hypothesis.  It is a clear and testable prediction of the present hypothesis that the undergoing SETI experiments using this conservative approach will yield only negative results.

(Italics theirs.)  How can their prediction indeed be tested?  If conventional SETI does get a radio signal, the prediction might fail; otherwise, how long would they have to wait in silence to feel vindicated?  Traditional SETI researchers would probably argue this point.  But Cirkovic and Bradley also put forth a falsification test: look for evidence of technological artifacts at the outer fringes of nearby galaxies.  That, unfortunately, will probably be very difficult without more advanced technology.  Nonetheless, they are quite adamant that traditional SETI thinking is parochial.  It’s oblivious to the physical constraints that would drive life toward information processing.  “In a sense the problem has nothing to do with the universe itself, and everything to do with our ignorance and prejudices,” they state accusingly.  “In this special sense, the flaws in the currently prevailing views on SETI are much less excusable.”
    In their paper, the authors acknowledged the contribution of Guillermo Gonzalez (along with Peter Ward and Donald Brownlee) to the extension of ideas about planetary “habitable zones” to galactic scales: the Galactic Habitable Zone (GHZ).2  They extended this concept further to a Galactic Technological Zone (GTZ), where machines could optimize their computational power.  This zone would be the outer reaches of a spiral galaxy – but not so far out that heavy elements would be lacking.  They were also honest about their assumptions:

There is no meaningful scientific hypothesis for resolving Fermi’s Paradox – or, indeed, any problem of importance in science – without a set of assumptions.  In building of the migrational solution to Fermi’s puzzle, we have relied on the following set of assumptions:

  1. The Copernican principle continues to hold in astrobiology, i.e. there is nothing special about the Earth and the Solar System when considerations of life, intelligent observers or ATCs are made.2
  2. Laws of physics (as applied to the classical computation theory and astrophysics) are universally valid.
  3. Naturalistic explanations for the origin of life, intelligence and ATCs are valid.
  4. The Milky Way galaxy exhibits well-established gradients of both baryonic matter density and equilibrium radiation field temperature.
  5. Habitable planets occur naturally only within the GHZ (which evolves in a manner roughly understood), but ATCs are not in any way limited to this region.
  6. We assume local influences both of and on ATCs.  Thus, we disregard overly speculative ideas about such concepts as cosmic wormholes or “basement universes”.  Interstellar travel is feasible, but it is bound to be slow and expensive (for anything larger than nanomachines) at all epochs.
  7. Astroengineering on the scales significantly larger than the scale of a typical planetary system (on the pc-scale and above) will remain difficult and expensive at all epochs and for all ATCs.
  8. ATCs will tend to maximize the efficiency of information-processing, no matter how heterogeneous their biological and cultural structures and evolutionary pathways are.

These assumptions are naturally of varying validity and importance.  Items 1 through 3 are essential methodological guidelines of the entire scientific endeavor.  Although item 1 has recently become controversial with “rare Earth” theorists, there is still no compelling reasons for relinquishing it.  Assumption 4 is an empirical fact, and 5 is quite close to it.  Assumptions 6 and 7 are conservative extrapolations of our limited scientific and technological perspective, but in our view should be retained until the contrary positions can be verified.  In particular, absence of the Galaxy-size astroengineering effects in external galaxies … strongly supports the assumption 7.

The most speculative assumption was #8, they acknowledged, but they reasoned this way: whether a civilization evolves toward hedonism (like the Romans) or toward accomplishment (like the Greeks), both would need to maximize their information processing.  “In either situation,” they rationalized, “they will seek the greatest computational capacity and efficiency possible to support these activities.”
    So there you have it.  The drive toward the ultimate CPU governs the fate of life and intelligence.  Geeks will someday rule the universe.


1Milan M. Cirkovic and Robert J. Bradbury, “Galactic gradients, postbiological evolution and the apparent failure of SETI,” New Astronomy, Volume 11, Issue 8, July 2006, Pages 628-639, doi:10.1016/j.newast.2006.04.003.
2See also the film The Privileged Planet.  In this film Gonzales discusses the GHZ, and Brownlee gives reasons for his “rare earth” hypothesis.  The film also argues against the assumed Copernican Principle.

Interesting paper.  Heavily sci-fi, profoundly speculative, politically incorrect, and somewhat amusing, perhaps, but thought-provoking.  Is it scientific?  Does its presence in a scientific journal indicate it is worthy of more serious consideration by rational truth-seekers than if it appeared in a theological journal or in Mad Magazine?  After all, they made predictions and provided a falsification criterion.  They talked about baryons and physical laws and thermodynamics.  And look – they even had equations!  Surely no one could accuse this kind of sober, rigorous analysis as being equivalent to religion.  What do you think?
    Religion is a misleading word in this context.  It conjures up images of candles, robes, icons and prayer wheels.  World view is a more appropriate term: a way of looking at the world, of answering the big questions: who are we?  Where did we come from?  Why are we here?  Where are we going?  Science cannot answer these questions, yet world-view issues loom big in this article.  They have attempted to give their opinion about the origin and ultimate fate of the universe, dress it in a lab coat and pass it off as science.  Yet by any measure of scientific criteria, they always left a way out.
    Their prediction is hollow, because it would require proving a universal negative.  Their falsification test is hollow, because we could all be dead before anyone finds a way to detect an unknown kind of technology at intergalactic distances, and even if someone did, another would find a natural explanation for it.  Predictions and falsifiability are not necessary components of science anyway, according to some philosophers of science.  And equations – well, nice, but the ones in the paper describe observable physical properties of temperature distribution in galaxies and have nothing to do with the social habits of intelligent beings.  Sentient beings are notoriously resistant to obeying equations about what they should do or will do.  In short, the scientific props of this article are distractions from the fact this is nothing more than a world view paper.
    Their entire thesis breaks down on one of their assumptions.  It was nice of them to list their assumptions, but not so nice to glibly claim that the least plausible is one of “essential methodological guidelines of the entire scientific endeavor,” namely, “Naturalistic explanations for the origin of life, intelligence and ATCs are valid.”  Did you catch it?  They just attempted to baptize naturalism in the waters of science as if we wouldn’t notice.  (Only Cirkovic has a PhD, but they both attempted to doctor a philosophy.)
    Why should this tactic be allowed for sci-fi speculation, but not for other kinds of scholarly investigation?  After all, theologians can make testable predictions.  A conservative Bible scholar, for instance, could predict that evidence for King David will be found, even point to the Tel Dan inscription as confirming evidence.  Some preachers argue that the equation “nothing times nobody equals everything.” has been falsified.  Should sufficiently scholarly sermons be allowed in scientific journals, then?  Not a few theologians are well trained in mathematical physics, and not a few scientists doubt the assumptions listed by these two speculators.  They should have no privilege in this game.  The quality of the reasoning and the support of evidence, not the scientific trappings and venue, need to carry weight in evaluating world view claims.  Cirkovic and Bradbury may wish to believe that life and intelligence are emergent properties of matter in motion, but they cannot support this world view with scientific evidence.  In fact, the tide of evidence is overwhelmingly against it (06/12/2006, 04/17/2006, online book).
    These sci-fi speculators pulled off a shifty sidestep.  They merely assumed that “naturalistic explanations” for these things are “valid,” and then hid behind an arbitrary rule that naturalism is an essential methodological guideline for the entire scientific endeavor.  Oh yeah?  It wasn’t for many of the greatest scientists in history (see online book).  This claim is only made now by the Eugenie Scotts and Ken Millers of the world who want to shield their philosophical speculations from critical scrutiny.  It’s a tactic not unlike the childhood ploy “King’s X” that allows them to evade rules of the game to which the others are bound.
    Cirkovic and Bradbury are as free as anyone to speculate, but need to take their speculations out of New Astronomy and argue them before philosophers and theologians, not claim special privilege for things that cannot be observed or known – indeed, things that run contrary to what we do know about the propensities of matter in motion.  What they wrote, though, is bound to make the SETI Institute angry.  A lot of investment capital is bound up in traditional SETI strategies.  These two warring parties may make any further comments superfluous; they may end up falsifying each other.

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